Heater for vacuum pump



1966 F. J. ERHART ETAL 3,

HEATER FOR VACUUM PUMP Filed April 19, 1963 4 Sheets-Sheet 1 Jan. 4, 1966 F. J. ERHART ETAL 3,227,361

HEATER FOR VACUUM PUMP Filed April 19, 1963 4 Sheets-Sheet 2 i M a Jan. 4, 1966 F. J. ERHART ETAL 3,

HEATER FOR VACUUM PUMP Filed April 19, 1965 4 Sheets-Sheet 5 w lzilza Jan. 4, 1966 F. J. ERHART ETAL 3,227,361

HEATER FOR VACUUM PUMP United States Patent 0 3,227,361 HEATER FOR VACUUM PUMP Francis J. Erhart, Rochester, and Matthew W. Davis, Jr., Macedon, N.Y., assignors to Consolidated Vacuum Corporation Filed Apr. 19, 1963, Ser. No. 274,215 8 Claims. (Cl. 230101) The present invention relates to vacuum pumps and, more particularly, to an improved heater for diffusion type vacuum pumps.

Difiusion pumps for establishing high vacua are well known. In general, these pumps comprise a scalable housing, means for supplying a charge of liquid, such as oil, to such housing, a pumping nozzle assembly located in the housing above the liquid charge, and a hollow vapor-conducting jet element extending from the liquid charge to the nozzle assembly. During operation, the pump is normally connected between a mechanical forepump and the space or vessel to be evacuated. The liquid charge is then heated to a temperature resulting in the release of vapor. The aforesaid jet element, or other suitable structure, conducts these resulting vapors to the nozzle assembly which is designed to form streams of vapor forcing gas molecules to be pumped to the above-mentioned forepump.

The present invention provides improved structure for heating the aforesaid liquid charge and improving the release of pumping vapor therefrom.

More specifically, the invention provides a heat-transfer structure extending through the aforesaid liquid charge for transferring heat to the liquid charge and projecting into the above-mentioned jet element or, generally, above the liquid charge for transferring heat to the inside of the hollow jet element or, generally, for heating the space above the liquid charge. The heat-transfer structure is maintained in heat-transfer relation with a suitable heating means, such as one or more electrically energized heating elements, which supply heat energy to the heat-transfer structure so as to cause boiling of the liquid and heating of the vapors emerging therefrom.

In accordance with a primary feature of the invention, the heat-transfer structure defines or is provided with a plurality of spaced perforations or openings permitting substantially free movement of the liquid through the heat-transfer structure.

The expression substantially free movement is meant to refer to liquid flow in a manner so that a subdivision of the liquid into relatively distinct areas by the elements of the heat-transfer structure is avoided or largely eliminated.

'In other words, the number, size and relative spacing of the perforations is such that the heat-transfer structure will not severely impede the flow of liquid throughout the liquid charge.

Accordingly, the latter perforations may be arranged in the form of two-dimensional patterns covering the heattransfer structure or the elements thereof.

It will now be appreciated that the invention provides a heating or heat-transfer means in which the liquid can distribute itself relatively freely in accordance with the thermal gradients existing or occurring in the liquid charge during the heating process. At the same time, the invention also provides a means for transferring or dissipating heat energy to the vapors emerging from the liquid charge, which will result in an improved pumping vapor formation.

In a preferred embodiment of the invention, the aforesaid perforations are formed by punching tabs out of the material of the heat-transfer structure. This not only provides these perforations but also forms a plurality of heat-dissipating fins which assist the liquid and vapor heating function of the heat-transfer structure.

3,227,361 Patented Jan. 4, 1966 ice Alternatively, the perforated heat-transfer structure may be provided with separate heat-dissipating fins which may also be provided with a large number of substantially uniforrnly distributed perforations or openings.

In a further preferred embodiment of the invention, the heat-transfer structure includes a plurality of substantially cylindrical, concentric heat-transfer elements each defining apertures or openings arranged in the aforesaid manner or pattern. Preferably, each heat-transfer element has punched-out tabs of the aforesaid type or has heat-transfer or dissipating fins associated in heat-transfer relation therewith. These tabs or fins may extend substantially radially with respect to the concentrical heat-transfer elements.

In an additional preferred embodiment, the latter fins are provided by a corrugated fin structure disposed between and in heat-transfer relationship with adjacent heattransfer elements. In accordance with the invention, this corrugated fin structure also defines a plurality of apertures distributed in a substantially uniform, two-dimensional pattern over the fin structure.

Heat energy may be supplied to the heat-transfer structure or elements in various ways.

Thus, in a preferred embodiment of the invention, the pump housing is provided with a bottom of heat-conductive material and the heat-transfer structure or elements are located so as to extend from such bottom. Suitable heating elements, such as metal-clad electric resistance heaters, are provided in heat-transfer relation with such bottom. This may be done by embedding such elements in the heat-conductive bottom or by attaching such elements to the lower surface of the heat-conductive bottom.

In accordance with an additional feature of the invention, the means for supplying heat energy to the heattransfer structure or elements may comprise a plurality of sector-shaped or pie-shaped heating elements distributed over the lower surface of the heat-conductive bottom. Elements of this type are easily installed and removed and afford an even heat distribution over the heatconductive bottom and adjacent parts.

The invention will be more readily apparent from the following detailed description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings, in which:

FIG. 1 shows an elevation, partially in section, of a diffusion pump embodying the invention;

FIG. 2 shows, on an enlarged scale, a top view along lines 11-11 of FIG. 1;

FIG. 3 shows a section along lines III--IlI of FIG. 2;

FIG. 4 shows a detail of the structure shown in FIGS. 1 to 3;

FIG. 5 shows a detail of a modification of the diffusion pump shown in FIGS. 1 to 3, in a view similar to that of FIG. 2;

FIG. 6 shows a section along line VIVI of FIG. 5; and

FIG. 7 shows a bottom view of FIG. 1 with a modified heating structure.

The diffusion pump shown in FIG. 1 has a housing 10 having a lateral wall 11 delimiting an internal pump chamber 12. One end of wall 11 is provided with a flange 14 for connection of the diffusion pump to a space or vessel to be evacuated (not shown). An outlet pipe stud 15 for connection of the difiusion pump to a mechanical forepump or similar means (not shown) is arranged in the vicinity of the other end of wall 11. A conventional vacuum pumping nozzle assembly 17 is arranged and mounted in pump chamber 12. Since structcre and function of such nozzle assembly are well known and since the nozzle assembly per se does not form part of the invention, it has only been indicated schematically in dotted lines in FIG. 1 to show its position in chamber 12.

At the lower portion thereof, housing includes a bottom 19 of heat-conductive material. Bottom 19 is connected to a flange 20 on wall 11 by means of nut and bolt arrangements 21. A seal member schematically shown at 22 is interposed between bottom 19 and flange 20.

In the shown embodiment, bottom 19 is provided with a dome structure 24. Dome structures of this type are conventional and are frequently employed in diffusion pumps of the subject class to reduce the liquid charge and to influence the vapor distribution in the pump.

A supporting base member 25 is attached to the lower surface of bottom 19. A pipe member 28 connected to a suitable source (not shown) of liquid, such as oil, extends through base member 25 and bottom 19 and serves as a means for supplying a charge of liquid 30 to housing 10. As shown, this charge of liquid is deposited on the upper surface 31 of bottom 19. A hollow jet element 33 is slightly immersed in liquid charge 30 and is connected to nozzle arrangement 17.

A coiled metal-clad electric heating element 34 is attached in good heat-transfer relation to the lower surface 26 of bottom 19, such as by welding or brazing. Heating element 34 extends to a suitable receptacle 35 for connection thereof to a source of electric power (not shown).

A heat-transfer structure 37 designed in accordance with the principles of the subject invention extends from bottom 19 through liquid charge 30 and projects into the space within hollow jet element 33 or, generally speaking, projects above liquid charge 30.

Details of heat-transfer structure 37 are more readily apparent from FIGS. 2 and 3.

In the embodiments shown in FIGS. 1 to 3, heat transfer structure 37 is composed of four cylindrical, concentric heat-transfer elements 40, 41, 42, and 44, which are inserted in corresponding grooves 46, 47, 48, and 49 in bottom 19, so that there is good heat conduction from bottom 19 to elements 40, 41, 42, and 44. It would, of course, also be possible to secure this heat conduction by attaching elements 40, 41, 42, and 44 to upper surface 31 of bottom 19.

At any rate, the heat-transfer elements 40, 41, 42, and 44 extend from heated bottom 19 through liquid charge 30 to a location above liquid charge 30. Each of the elements 40, 41, 42, and 44 has a large number of heattransfer and dissipation fins 50 projecting therefrom. These fins 50 are formed by punching out tabs 50 from the elements 40, 41, 42, and 44. The punching out of these tabs 50 will also provide elements 40, 41, 42, and 44 with a large number of openings or perforations 52. Considering the location of tabs 50 apparent from FIGS. 2 and 3, it will be readily appreciated that the perforations 52 in each element 40, 41, 42, and 44 are substantially uniformly distributed over such element in a twodimensional pattern, i.e. a pattern extending along the height of each element and peripherally therealong.

The latter arrangement of apertures 52 is also apparent from FIG. 4 which shows, in elevation, a portion of element 40 removed from the structure shown in FIGS. 2 and 3.

During operation of the diffusion pump illustrated in FIGS. 1 to 4, heating element 34 is energized and releases heat energy. This heat energy permeates bottom 19 and heat-transfer elements 40, 41, 42, and 44 including fins thereof. Elements 40, 41, 42, and 44 and certain of their fins 50 transfer the heat energy to the liquid charge 30 and cause boiling thereof. During this boiling operation, the liquid in charge 30 is free to flow substantially unimpeded through transfer elements 40, 41, 42, and 44, that is through perforations 52 which occupy a large portion of elements 40, 41, 42, and 44. In this fashion, the formation of localized liquid pockets between elements 40, 41, 42, and 44 is avoided and the liquid will be able to flow freely past heat-transfer fins 50, which will result in a uniform heat distribution across liquid charge 30, substantially free of widely differing thermal gradients. In addition, the projecting portions of elements 40, 41, 42, and 44 with the associated fins 50 will also dissipate substantially evenly distributed heat into the space above liquid charge 30 and will thus convey heat energy to the surface of liquid charge 30 and to the vapors emerging therefrom. In this manner, a steady supply of vapor of high energy content is produced for the nozzle assembly 17, and an improved pumping operation is achieved.

If desired, the fins 50 or tab portions 50 may be omitted from the structure shown in FIGS. 1 to 4, provided the remaining perforated elements 40, 41, 42, and 44 are supplied with sufficient heat energy to perform their aforedescribed function. In this case, the apertures or openings 52 could be formed by a type of punching operation which leaves no tabs.

FIGS. 5 and 6 show a first modification of the structure illustrated in FIGS, 1 to 4. Certain elements of FIGS. 5 and 6 which are identical to those shown in FIGS. 1 to 4 are provided with the corresponding reference numerals employed hereinbefore.

The heat-transfer structure 60 of FIGS. 5 and 6 comprises three spaced, cylindrical and concentric heattransfer elements 61, 62, and 63 extending from bottom 19 through liquid charge 30 and projecting into the space above liquid charge 30. These elements 61 to 63 again define a large number of perforations, indicated in FIG. 6 at 65, arranged in two-dimensional patterns extending over elements 61 to 63. A corrugated or zigzag-type fin structure 66 is disposed between elements 61 and 62 and has portions thereof in heat-transfer relation therewith. Similar fin structures 67 and 68 are disposed between elements 62 and 63 and adjacent element 63, respectively. To assure a reliable transfer of heat, the peaks and valleys of fin structures 66 to 68 may be brazed or welded, such as spot welded, to the respective elements 61 to 63.

As shown, the fin structures 66 to 68 are also provided with uniformly distributed apertures, indicated at 70. These apertures are also arranged in two-dimensional patterns, so as to permit passage therethrough of the liquid in charge 30 and of part of the vapors above charge 30.

Bolts, one of which is shown in FIGS. 5 and 6 at 72, are employed to maintain heat-transfer structure 60 in abutting engagement with bottom 19. As shown, bolt 72 has associated therewith a washer 73 bearing against elements 62 and 63 and has an outer thread 74 engaging a corresponding threaded bore 75 in bottom 19.

If desired, elements 61 to 63 could, of course, be fitted into corresponding grooves in bottom 19 similar to grooves 46 to 48 shown in FIG. 3.

FIG. 6 shows the heating element 34 embedded in bottom 19. While this expedient could also be employed in the embodiment of FIGS. 1 to 4, heating element 34 could, in the structure shown in FIG. 6, also be attached to the lower surface 26 of bottom 19.

At any rate, the operation of the structure shown in FIGS. 5 to 6 is similar to that of the embodiment of FIGS. 1 to 4. Thus, the large number of apertures and will again permit flow of liquid throughout charge 30 and the projecting portions of elements 61 to 63 and fin'structures 66 to 68 will again promote the continuous supply of high-energy vapor to pumping nozzle structure 17.

As far as the positioning of heating element 34 is concerned, it will be appreciated that the heat dissipation of heating element 34 is improved if such element is embedded in heat-conductive bottom 19 of housing 10.

On the other hand, a heating element that is merely attached to bottom 19 is more readily replaced if defective.

However, the conventionally employed heater elements of the tubular type have the disadvantage of presenting but a relatively small heat-transfer surface to bottom 19 when merely attached thereto.

A heater element structure which overcomes the latter disadvantage and is readily installed on and removed from the outer surface 26 of bottom 19 is shown in FIG. 7.

Thus, FIG. 7 illustrates a heater structure 80 comprised of six individually removable heating elements 81, 82, 83, 84, 85, and 86 having a sector or pie-shaped type of configuration. Each heating element has an electric resistance heater arrangement diagrammatically indicated in FIG. 7 at 88, a pair of terminals 90 and 91, and a body 93 embedding resistance heater 88 and mounting terminals 90 and 91. Body 93 comprises heat-conductive material assuring good heat-transfer from resistance heater 88 to bottom 19. Heating elements 81 to 86 are individually attached to bottom 19 by means of removable bolts 95 which engage tapped bores (not shown) in bottom 19.

An electric circuit through resistance heaters 88 is completed by conductors 100, 101, 102, 103, 104, 105, and 106. Conductors 100 and 106 may be connected to a suitable source of electric power (not shown). If desired, the parts of body 93 of each heating element not in contact with bottoms 19 may be provided with or comprised of heat-insulating material to reduce undue heat dissipation therefrom.

The heater structure 80 can, of course, be composed of any number of elements. In any case, it will be appreciated that heater structure 80 provides a superior heat generating means for the diffusion pumps discussed and is easily partially or completely replaced when defective.

While certain embodiments of the invention have been shown and illustrated, it will be readily appreciated that various modifications thereof are possible without departure from the scope of the subject invention.

Thus, the numbers of heat-transfer elements could, of course, be smaller or greater than illustrated. Also, the mutual spacing of the heat-transfer elements need, of course, not necessarily be uniform throughout the heattransfer structure.

In addition, heat-transfer elements having apertures formed by bending rather than punching out portions thereof could be utilized.

Also, the dome structure of the type of dome 24 could be replaced by other liquid displacing means or could be eliminated. In the latter case, the parts of the heattransfer structure could be distributed over a larger portion of the liquid charge.

It would also be possible to assemble the heat-transfer elements of FIGS. 1 to 4 into a unitary structure to perunit ready insertion and removal thereof.

Furthermore, heating means other than the heater elements or structures described could, of course, be employed in connection with the subject heat-transfer structure or elements.

Other modifications or variations within the scope of the invention will be apparent to those skilled in the art.

We claim:

1. A diffusion pump comprising a housing including a bottom of heat-conductive material and lateral wall portions, means for depositing a charge of liquid to be evaporated on said bottom of said housing, a pumping nozzle assembly located within said lateral wall portions and connected to the space above said charge of liquid, at least two spaced, substantially cylindrical, concentric heattransfer elements extending from said bottom through said liquid charge to a location above said liquid charge, a fin structure disposed between and in heat-transfer relation with said spaced heat-transfer elements, said heattransfer elements and said fin structure each defining a plurality of apertures disposed in two-dimensional patterns over said heat-transfer elements and said fin structure, and a heating element structure in heat-transfer relation with said heat-conductive bottom.

2. A diffusion pump comprising a housing including a bottom of heat-conductive material and lateral wall portions, means for depositing a charge of liquid to be evaporated on said bottom of said housing, a pumping nozzle assembly located within said lateral wall portions and connected to the space above said charge of liquid, at least two spaced, substantially cylindrical, concentric heat-transfer elements extending from said bottom through said liquid charge to a location above said liquid charge, a corrugated fin structure disposed between and in heat-transfer relation with said spaced heat-transfer elements, said heat-transfer elements and said fin structure each defining a plurality of apertures disposed in twodimensional patterns over said heat-transfer elements and said fin structure, and a heating element structure in heattransfer relation with said heat-conductive bottom.

3. A diffusion pump comprising a housing including a bottom of heat-conductive material having an upper surface and lower surface, and lateral wall portions defining a chamber above said upper bottom surface, means for depositing a charge of liquid to be evaporated on said upper bottom surface, a pumping nozzle assembly located in said chamber and connected to the space above said liquid charge, a plurality of substantially cylindrical, concentric heat-transfer elements extending from said bottom through said liquid charge to a location above said liquid charge, each of said heat-transfer elements defining a plurality of space perforations distributed in two-dimensional patterns over the heat-transfer elements to permit substantially free liquid flow through said heat-transfer elements, and a plurality of sector-shaped heating elements in heat-transfer relation with and distributed over said lower bottom surface.

4. A diffusion pump comprising a housing including a bottom of heat-conductive material having an upper surface and a lower surface, and lateral wall portions defining a chamber above said upper bottom surface, means for depositing a charge of liquid to be evaporated on said upper bottom surface, a pumping nozzle assembly located in said chamber and connected to the space above said liquid charge, a plurality of substantially cylindrical, concentric heat-transfer elements extending from said bottom through said liquid charge to a location above said liquid charge, each of said cylindrical heat-transfer elements including a plurality of substantially radially extending fins formed by tab portions punched out of the material of the heat-transfer elements, and a plurality of sector-shaped heating elements in heat-transfer relation with and distributed over said lower bottom surface.

5. A diffusion pump comprising a housing including a bottom of heat-conductive material having an upper sur face and a lower surface, and lateral wall portions defining a chamber above said upper bottom surface, means for depositing a charge of liquid to be evaporated on said upper bottom surface, a pumping nozzle assembly located in said chamber and connected to the space above said liquid charge, at least two spaced, substantially cylindrical, concentric heat-transfer elements extending from said bottom through said liquid charge to a location above said liquid charge, a fin structure disposed between and in heat-transfer relation with said spaced heat-transfer elements, said heat-transfer elements and said fin structure each defining a plurality of apertures disposed in twodimensional patterns over said heat-transfer elements and said fin structure, and a plurality of sector-shaped heating elements in heat-transfer relation with and distributed over said lower bottom surface.

6. A diffusion pump comprising a housing, means for supplying a charge of liquid to be evaporated to said housing, a pumping nozzle assembly located in said housing above said liquid charge and connected to the space above said liquid charge, a plurality of spaced heattransfer elements extending through said liquid charge for transferring heat to said liquid and projecting into the space above said liquid charge for dissipating heat into said space, adjacent pairs of said heat-transfer elements defining channels wherein said liquid charge is located, a plurality of heat-transfer fins connected at least to alternate heat-transfer elements, said heat-transfer fins extending from said elements into each of said channels and defining a plurality of passages Within each channel, each of said heat-transfer elements defining a plurality of openings therethrough for permitting liquid flow through said heat-transfer elements into adjacent channels and to at least part of said heat-transfer fins, and heating means in heat-transfer relation with said heat-transfer elements for supplying heat energy to said heat-transfer elements.

7. A diffusion pump comprising a housing, means for supplying a charge of liquid to be evaporated to said housing, a pumping nozzle assembly located in said housing above said liquid charge and connected to the space above said liquid charge, a plurality of spaced heattransfer elements extending through said liquid charge for transferring heat to said liquid and projecting into the space above said liquid charge for dissipating heat into said space, adjacent pairs of said heat-transfer elements defining channels wherein said liquid charge is located, at least alternate heat-transfer elements having a plurality of punched-out tabs with adjacent perforations arranged in a two-dimensional pattern extending over each heattransfer element from a point within said liquid charge to a point above said liquid charge, said tabs extending from said elements into said channels and defining a plurality of passages for permitting liquid flow within each channel, and heating means for supplying heat energy to said heat-transfer elements and to said liquid charge.

8. A diffusion pump comprising a housing including a bottom of heat-conductive material and lateral wall portions, means for depositing a charge of liquid to be evaporated on said bottom of said housing, a pumping nozzle assembly located within said lateral wall portion and connected to the space above said charge of liquid, a plurality of substantially cylindrical concentric heattransfer elements extending from said bottom through said liquid charge to a location above said liquid charge, adjacent pairs of said heat-transfer elements defining channels wherein said liquid charge is located, each of said cylindrical heat-transfer elements including a plurality of substantially radially extending fins formed by tab portions punched out of the material of the heattransfer elements, said tab portions defining a plurality of passages within said channels for permitting liquid fiow within said channels, the heat-transfer elements defining a plurality of openings therein where the tab portions were punched out for permitting liquid fiow between adjacent channels, and a heating element structure in heattransfer relation with said heat-conductive bottom.

References Cited by the Examiner UNITED STATES PATENTS 2,013,914 9/ 1935 Hartmann. 2,437,849 3/1948 Cox et al. 23010l 2,943,783 7/1960 Bancroft et a1 230101 3,046,758 7/1962 Heuer et al. 3,075,687 1/1963 Stevenson 230101 FOREIGN PATENTS 289,218 12/1915 Germany.

DONLEY J. STOCKING, Primary Examiner.

WARREN E. COLEMAN, LAURENCE V. EFNER,

Examiners. 

1. A DIFFUSION PUMP COMPRISING A HOUSING INCLUDING A BOTTOM OF HEAT-CONDUCTIVE MATERIAL AND LATERAL WALL PORTIONS, MEANS FOR DEPOSITING A CHARGE OF LIQUID TO BE EVAPORATED ON SAID BOTTOM OF HOUSING, A PUMPING NOZZLE ASSEMBLY LOCATED WITHIN SAID LATERAL WALL PORTIONS AND CONNECTED TO THE SPACE ABOVE SAID CHARGE OF SAID LIQUID, AT LEAST TWO SPACED, SUBSTANTIALLY CYLINDRICAL, CONCENTRIC HEATTRANSFER ELEMENTS EXTENDING FROM SAID BOTTOM THROUGH SAID LIQUID CHARGE TO A LOCATION ABOVE SAID LIQUID CHARGE, A FIN STRUCTURE, DISPOSED BETWEEN AND IN HEAT-TRANSFER RELATION WITH SAID SPACED HEAT-TRANSFER ELEMENTS, SAID HEATTRANSFER ELEMENTS AND SAID FIN STRUCTURE EACH DEFINING A PLURALITY OF APERTURES DISPOSED IN TWO-DIMENSIONAL PATTERNS OVER SAID HEAT- TRANSFER ELEMENTS AND SAID FIN STRUTURE, AND A HEATING ELEMENT STRUCTURE IN HEAT-TRANSFER RELATION WITH SAID HEAT-CONDUCTIVE BOTTOM. 